The existing shoulder strap chest system for a pack, as shown in FIG. 2, consists of slipping ladders 9, 10 at left side strap 14 and right side strap 15 respectively, and a middle fastener 11 for adjusting the connecting strap 12. The connecting strap 12 is connected to two shoulder pads 16, 17. The left side strap 14 and the right strap 15 are sewn on the shoulder pads 16, 17 respectively. The existing shoulder strap chest system is disadvantageous in that slipping ladders 9, 10 are not available for free attachment and can slip on the strap of the shoulder pad, which brings about troubles to users.